Inkjet technology has expanded its application to high-speed, commercial and industrial printing, in addition to home and office usage, because of its ability to produce economical, high quality, multi-colored prints. This technology is a non-impact printing method in which an electronic signal controls and directs droplets or a stream of ink that can be deposited on a wide variety of substrates. Inks used in such technologies can be liquid dispersions, solution, or emulsions and can include oil-based inks, non-aqueous solvent based inks, water-based inks and solid inks. Current inkjet printing technology involves forcing the ink drops through small nozzles by thermal ejection, piezoelectric pressure or oscillation, onto the surface of a media. The deposited ink droplets are, then, dried, e.g., using heat or forced air, or allowed to dry at ambient conditions.
Recently, curing of ink by radiation and, in particular, ultraviolet (UV) curing, has become popular. In these cases, special ink is used and the image is cured by exposure to a radiation source. The uses of such radiation-curable (or photo-curable) inks and the curing process are rapidly becoming an alternative to the established conventional drying process.
The inkjet printing industry uses different types of recording fluids such as oil-based inks, solvent-based (non-aqueous) inks, water-based inks and solid inks (which are melted in preparation for dispensing). Solvent-based inks are fast drying and, as a result, are widely used for industrial printing. When solvent-based inks containing binders and other ingredients are jetted onto a substrate, the solvent(s) partially or fully evaporate from the ink, leaving the binder and other ingredients such as pigment particles on the printed substrate in the form of a dry film. During the drying process, the solvents, which are often volatile organic compounds (VOC), emit vapors and, therefore, can pollute the environment. The pollution problem becomes more critical for higher printing speeds or for wide format images, where large amounts of ink are deposited onto a substrate.
As a result of this and other concerns, efforts related to preparing inks that are environmentally friendly have moved some research in the direction of water-based inks. However, radiation-curable (or photo-curable) water-based ink compositions are noticeably limited among available options due to their specific features. Accordingly, investigations continue into developing radiation-curable water-based ink compositions that exhibit, when printed, specific and excellent printing properties as well as improved stability.